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8N51 Timing

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Btzj02
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PostPosted: Mon Jun 08, 2020 1:34 pm    Post subject: 8N51 Timing Reply to specific post Reply with quote

Need help with the next step. Suggestions please. Today I was determined to trouble shoot the irritating intermittent missing or poofing in the exhaust. I have narrowed down my problem to the #2 cylinder. I replaced the spark plug and did a spark test. Good spark, greater than 1/4 inch. I attached the timing light to #1 cylinder and that was at 4 degrees at idle. So timing "appeared" to be good.

I then checked the timing of #2 cylinder and it was all over the map, most of the time greater than 10 degrees. Cylinders 3 and 4 were consistently within a degree or two of the #1 cylinder. The results are repeatable.

I have the original side distributor and the ears on the cam do look worn. I did have to do a lot of work on the advance weights to free them up but they seem to be working ok now. Is my next step a distributor rebuild/replace or is there something else I can rule out?
Thank for any ideas JB
 
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Bruce(VA)
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PostPosted: Mon Jun 08, 2020 1:53 pm    Post subject: Re: 8N51 Timing Reply to specific post Reply with quote

Just because I’ve never experienced a worn out distributor cam doesn’t mean it can’t happen.


Sidemount measurements are:

Across flats = .72
Over lobes = .78 dia.
75 Tips

 
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Rusty2N
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PostPosted: Mon Jun 08, 2020 3:48 pm    Post subject: Re: 8N51 Timing Reply to specific post Reply with quote

Did you do a compression test?
 
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Den N Ms
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PostPosted: Mon Jun 08, 2020 4:33 pm    Post subject: Re: 8N51 Timing Reply to specific post Reply with quote

Btzj02 ,Please explain to me how you come up with 10% with a timing light on #2 and #3 cylinders.I would like to know.
 
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wore out
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PostPosted: Mon Jun 08, 2020 4:53 pm    Post subject: Re: 8N51 Timing Reply to specific post Reply with quote

Btzj02 wrote:
(quoted from post at 14:34:05 06/08/20) Need help with the next step. Suggestions please. Today I was determined to trouble shoot the irritating intermittent missing or poofing in the exhaust. I have narrowed down my problem to the #2 cylinder. I replaced the spark plug and did a spark test. Good spark, greater than 1/4 inch. I attached the timing light to #1 cylinder and that was at 4 degrees at idle. So timing "appeared" to be good.

I then checked the timing of #2 cylinder and it was all over the map, most of the time greater than 10 degrees. Cylinders 3 and 4 were consistently within a degree or two of the #1 cylinder. The results are repeatable.

I have the original side distributor and the ears on the cam do look worn. I did have to do a lot of work on the advance weights to free them up but they seem to be working ok now. Is my next step a distributor rebuild/replace or is there something else I can rule out?
Thank for any ideas JB


The "wear block" on the points isn't as "wide" as the point cam lobes, so wear would show up as a sort of wide "groove" in the face of the cam lobe with unworn cam profile "above" and/or "below" the worn area.

Have you looked closely at the #2 lobe?

I would suspect a worn distributor bushing and shaft, would cause the timing to "jump around" before I would suspect a worn cam lobe.

Could even have a bend to it, and flopping around.

Also, if the camshaft (for some reason) is moving fore and aft a bit that can cause "spark scatter" due to the angle-cut camshaft drive gears and angle-cut distributor drive gears. (Helical geartrins.)
 
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Denny K
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PostPosted: Mon Jun 08, 2020 5:09 pm    Post subject: Re: 8N51 Timing Reply to specific post Reply with quote

I hope he answers that question! I have been timing engines for over 55 years (even 600 + hp racing
engines) and have never heard of timing any cylinder but #1.
 
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R Geiger
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PostPosted: Mon Jun 08, 2020 5:18 pm    Post subject: Re: 8N51 Timing Reply to specific post Reply with quote

CVPost-denny k wrote:
(quoted from post at 19:09:12 06/08/20) I hope he answers that question! I have been timing engines for over 55 years (even 600 + hp racing
engines) and have never heard of timing any cylinder but #1.

I have read that there are two sets of timing marks on the flywheel so that one could time the engine from any cyclinder.
 
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R Geiger
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PostPosted: Mon Jun 08, 2020 5:36 pm    Post subject: Re: 8N51 Timing Reply to specific post Reply with quote

Den N Ms wrote:
(quoted from post at 18:33:13 06/08/20) Btzj02 ,Please explain to me how you come up with 10% with a timing light on #2 and #3 cylinders.I would like to know.
According to FO-4 that is why there are two sets of timing marks on the flywheel.
 
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lha
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PostPosted: Mon Jun 08, 2020 6:28 pm    Post subject: Re: 8N51 Timing Reply to specific post Reply with quote

This may not be your problem,but on my 9n,while setting my points I noticed that the gap was different[though slightly] on
different lobes. I set the gap on the lobes so they all had at least the minimum gap. I replaced the bushings on the shaft
and it ran more smoothly.
 
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JMOR
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PostPosted: Mon Jun 08, 2020 8:08 pm    Post subject: Re: 8N51 Timing Reply to specific post Reply with quote

Btzj02 wrote:
(quoted from post at 17:34:05 06/08/20) Need help with the next step. Suggestions please. Today I was determined to trouble shoot the irritating intermittent missing or poofing in the exhaust. I have narrowed down my problem to the #2 cylinder. I replaced the spark plug and did a spark test. Good spark, greater than 1/4 inch. I attached the timing light to #1 cylinder and that was at 4 degrees at idle. So timing "appeared" to be good.

I then checked the timing of #2 cylinder and it was all over the map, most of the time greater than 10 degrees. Cylinders 3 and 4 were consistently within a degree or two of the #1 cylinder. The results are repeatable.

I have the original side distributor and the ears on the cam do look worn. I did have to do a lot of work on the advance weights to free them up but they seem to be working ok now. Is my next step a distributor rebuild/replace or is there something else I can rule out?
Thank for any ideas JB
" Cylinders 3 and 4 were consistently within a degree or two of the #1 cylinder." Sorry to burst your balloon, but in a 4 cyl engine, all 4 four fire with 2 revolutions, meaning cylinder to cylinder firing is 720/4=180 degrees apart, not "within a degree or two of #1".????????
 
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Welding man
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PostPosted: Tue Jun 09, 2020 4:03 am    Post subject: Re: 8N51 Timing Reply to specific post Reply with quote

You never owned a 345 International engine then. They timed on #8 Cyl.
 
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Btzj02
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PostPosted: Tue Jun 09, 2020 4:34 am    Post subject: Re: 8N51 Timing Reply to specific post Reply with quote

Due to my lack of experience and healthy curiosity I started checking the timing on all cylinders and Shazam! it is possible. The timing marks 180 degrees apart on the fly wheel allows this for 4 cylinder engine. My neighbor is a Farm All guy and he thought it sounds like an exhaust valve sticking. Pressure test was good last fall but I will test again today. Will also mic the cam on the distributor and see what I get.

My old Dodge Omni had a distributor but other then setting the points I don't remember much. What is considered normal for the contacts inside the Distributor cap and the rotor? There is a slight discoloration on the flat of the conductors that is flush with the distributor cap plastic. There is no discolorations on the conductor ear that protrudes into the distributor cap. The rotor also has a slight discoloration on the top of the conductor where the spark energy is transferred to the rotor cap. Question: is it possible the rotor is too high relative to the distributor cap?
 
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R Geiger
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PostPosted: Tue Jun 09, 2020 6:14 am    Post subject: Re: 8N51 Timing Reply to specific post Reply with quote

Do you have the clip installed under the rotor?
they are easy to lose.
If the rotor was too high it would hit the cap. the spring on the rotor rides on the carbon connector in the middle of the cap.
 
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Btzj02
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PostPosted: Tue Jun 09, 2020 6:52 am    Post subject: Re: 8N51 Timing Reply to specific post Reply with quote

[quote="CVPost-Bruce(VA)"](quoted from post at 14:53:47 06/08/20) Just because I ve never experienced a worn out distributor cam doesn t mean it can t happen.

Bruce, your record is intact. Measures as you indicate.
 
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Btzj02
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PostPosted: Tue Jun 09, 2020 9:19 am    Post subject: Re: 8N51 Timing Reply to specific post Reply with quote

CVPost-Rusty2N wrote:
(quoted from post at 16:48:39 06/08/20) Did you do a compression test?


New compression test complete. 105 to 110 psi on all cylinders.
 
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